Grinding wheel construction



1951 L. H. MlLLlGAN ET AL 2,537,541

GRINDING WHEEL CONSTRUCTION Filed July 19, 1945 2 Sheets-Sheet l PIGl Iiv

Lou/51.1. H. M/LL/GAN 20552.7 H. LaMamzp um m 17 Jan. 9, 1951 H.MILLIGAN ET AL 5 5 GRINDING WHEEL CONSTRUCTION Filed July 19, 1945 2Sheets-Sheet 2 loc- Lam/ELL h- MILL/6AM I ,Qoeser H-LoMsmzD PatenteclJan. 9, i951 GRINDING WHEEL GONSTRUCTION Loweii H. Milligan and RobertH. Lombard, Worcester, Mass., assignors to Norton Company, Worcester,Mass, a corporation of Massachusetts Application July 19, 1945, SerialNo. 605,97

9 Claims.

This invention relates to built-up grinding wheels and to a method ofconstructing them to overcome certain difficulties heretoforeencountered in interrelating the rigid, inflexible, bonded abrasiveelement and a rigid element which is to reinforce it or support it. 1

One of the objects of this invention is to provide a method and meansfor dependably securing together the relatively rigid or inflexible,bonded abrasive element, such as one in which the abrasive grains arebonded by a vitrified bond, and a companion element which is relativelyrigid or inflexible and which may serve as the support for the abrasiveelement or as a reinforcement for the rigid abrasive element. Frequentlythe supporting or reinforcing element is of metal, and frequently itserves principaliy or solely as a means for mounting the abrasiveelement, as, for example, upon a shaft, for rotation of the grindingwheel, and, particularly in such cases, the thermal coefficients ofexpansion are suihciently different so that the mere cementing togetherof the two is insufficient to cope with strains and stresses set up inthe junction when changes in temperature take place, as during the useof the grinding wheel. And such cementing cannot invariably be reliedupon to cope with strains and stresses setup in the junctionindependently of temperature change, such as, for

example, by centrifugal forces tending to rupture the grinding wheel ortending to displace the relatively heavy and rigid abrasive part.Various expedients have heretofore been resorted to in the endeavor toovercome such difficulties or deficiencies, but some of them arecumbersome and others require complicated procedures, and none of themovercomes the problems posed by, or the deficiencies and weaknesses in,the continuous face-to-face junction produced by known rigid cementingmethods. One of the dominant aims of this invention is to provide amechanical junction or union between such rigid elements of a grindingwheel that will overcome the difficulties and deficiencies such as thoseabove mentioned and to provide a practical and economical method ofachieving the same. Other objects will be in part obvious or in partpointed out hereinafter.

The invention accordingly consists in the features of construction,combination of elements, arrangements of parts, and in the several stepsand relation and order of each of the same to one or more of. theothers, all as will be illustratively described herein, and the scope ofthe ers, of suitable thickness, throughout which are application ofwhich will be indicated in the following claims.

In the accompanying drawings, in which are shown by way of illustrationseveral illustrative embodiments of the mechanical features of ourinvention, v

Fig. l is a vertical central sectional view through a composite orbuilt-up, rigid abrading tool in the form of a grinding wheel;

Fig. 2 is a fragmentary vertical sectional view, on a greatly enlargedscale, as seen along the line 2-2 of Fig. 1, showing certain features ofone embodiment of our invention;

Figs. 3 and 4 are transverse sectional views as seen along'the lines 33and 4A, respectively, of Fig. 2, being in effect greatly enlarged andsomewhat exaggerated fragmentary transverse. sections like the sectionof Fig. 1; l

Fig. B is a-transverse sectional view as seen along the line 3'---3 ofFig. 2, showing, in enlarged and somewhatv exaggerated form, certainpossible structural relationships of certain of the parts;

Fig. 5 is a fragmentary vertical sectional view, on a greatly enlarged.scale, as seen along the line 2-2 of .Fig. '1,.showing certain featuresofanother embodiment of 'ourrxinvention;,, i ;.r

Fig. 6 is a transverse sectional view as seen along the line B-6 of Fig.5, being in eifecta;

- greatly enlarged. and somewhat exaggerated 'vention.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

Our invention is best illustratedv with respect to the construction of aso-called cup wheel comprising a rigid or relatively inflexible abrasiveannulus or ring In, which may be assumed to comprise a body of ceramicor vitrified material by and throughout which the abrasive grains arebonded, or, in the case of diamond abrasive grains, may comprise one ormore external laydistributed and bonded the diamond abrasive grain, suchas the layer Hi and a body portion Hl united or integrally formedtherewith, as by utilizing a ceramic or vitrified bonding materialthroughout both portions; in the latter case the body portion 20 caninclude any suitable granular body material (abrasive or non-abrasive)bonded by the same or compatible vitrified bond as is used in the partIll In any such case, and for convenience, we term the member 10 as therigid or inflexible abrasive part; it and a companion member I I, alsoof rigid or inflexible material, are to be secured together, and, forpurposes of illustration, the member Il may be of metal, such as steelor cast iron, being provided with any suitable means, which may take anyone of a wide variety of known forms to mount or secure it to anappropriate part of the grind.- ing mechanism, such as a shaft, collar,hub, or

' the like.

In somewhat exaggerated form, there is indicated at !2 in Fig. l themeans forming the junction between the rigid parts [I] and II in oneembodiment, these are shown in larger scale in Fig. 3 and in anotherembodiment, in Fig. 6. They comprise a large number of substantiallyuniformly distributed, rigid and strong, individual masses which we termcolumns or posts, being indicated at H in Fig. 3 and also in Fig. 3 andat I3 in Fig. 6, and made of a hardened inflexible material which ispreferably of a character such that it can be applied, preferably in theabove-mentioned form of the columns or posts, in plastic state betweenthe adjacent faces of the rigid parts it) and II and thereafterhardened, cured, or matured in situ, the material having in plastic formappropriate qualities such as adhesiveness to join or bond itself, atthe respective ends of the posts, to the adjacent faces of the two rigidparts l and II.

The joining parts l3 and I?) are preferably of substantially uniformeffective cross-section; and in the form of Fig. 3 they are preferablyconnected as is better seen in Fig. 2 by laterally extending webs Mwhich may or may not, but preferably do, extend between the two faces ofthe rigid parts Ill and H, and which in either case can form laterallyextending cross-braces joining adjacent masses or columns [3.the-cross-connecting webs [4 do not engage with the faces of the rigidparts H] and I I, they would have the general conformation, andrelationship to the columns or posts, as is indicated in Fig. 3. Theyare made of the same material and when hardened they have qualitiesgenerally similar to those of the individual columns or posts H).Tog'ether the individual massesor columns l3 and their laterallyextending cross-connecting parts [4 have, in the cross-section as seenin Fig. 2, a grid-like conformation,-which, as later pointed out, may beof any desired pattern, preferably of substantially uniform geometricdesign or configuration, illustratively, as indicated in Fig. 2,comprising a succession'of substantially equal hollow squares with acolumn [3 at each apex thereof; within each of the squares is a hollowspace or cell l5 (see also Figs. 3 and 4) and these are thereforesubstantially uniformly distributed, representing voids, as betterappears in Figs. 3 and 4, so that the connecting and bridging materialbetween the rigid. parts l0 and ii is discontinuous, as seen along theline 2-2 of Fig. 1, and the cross-sectional area of the materialjoining' the parts Hi and H is thereby materially less than thecross-sectional area of either of the Where adjacent faces throughoutwhich it is desired to secure the two parts together. Where thecrossconnecting webs do not engage the adjacent faces of the rigid partsIt and II, as shown in Fig. 3 these spaces or cel.s 15 are connectedwith each other, to greater or less extent, by way of the gaps betweenthe webs l4 and the respective faces of the rigid parts Iii and H; thesegaps are clearly shown in Fig. 3

The material of which the bridging and securing means I2 is made ispreferably a resinous or synthetic resin composition having thecharacteristics above mentioned, being cured to hardened relativelyrigid or inflexible condition. As

' better appears in Figs. 3 and 4, the parts 13 and their connectedcross-bracing parts Hi are preferably of increasing cross-sectional areain both directions away from a central vertical plane which is indicatedat AA in Figs. 3 and 4, being in that respect outwardly divergent incross-section, and thus the parts l3 and the lateral crossconnectingparts 54 (where the latter engage the rigid parts H] and H) present tothe faces of the rigid parts H3 and Ii greater areas for strong bondingor adhesion to the faces of the parts than is its minimumcross-sectional area. In fact, the entire areas of adjacent faces of therigid parts ii) and H may in this manner he utilized, while retainingthe voids or cells I5, so as to achieve maximum area of junction of thesecuring means SE to the adjacent faces.

The rigid abrasive annulus l6 and the rigid part H are thus rigidlysecured together, and when forces are exerted, usually forces due todifferentials in the thermal coeflicients of expansion of the rigidparts Iii and ii, relative movement, vertically as viewed in Figs. 1, 3,and 4, tends to take place between the parts :8 and ii, subjecting theindividual rigid connecting masses to shear. Were the two rigid partssimply cemented together with a material that is hard and rigid uponsetting or curing, the magnitude and directions of such shear are suchthat the rigid abrasive annulus cracks, usually in radial directions,with the cracking commencing at the smallest radius of the rigidabrasive annulus; breakage of this character usually results when therigid abrasive annulus i0 is put into tension, that is, subjected toforces tending to increase its radii, and they can be brought about whenthe rigid part i i has a higher temperature coerlicient of expansionthat the rigid part I8, so that the part ll increases in radius fasterthan does the vitrified bonded annulus ill. Or the forces of shear, werethe rigid parts ii! and H to be rigidly secured together by a hardmaterial, can simply cause failure of the hard cemented junction byactual shear thereof in whole or in part.

Such destructive results as these are avoided according to ourinvention, for, when forces arise tending to subject, or actuallysubject, the connecting means l2 to shear, the individual bridging partsi3 thereof, laterally unsupported in the regions of the voids or cellsl5, can actually partake of bending and, though rigid and hard, arestrained or deformed in a manner analogous, for example, to thedeformation that a rigid, structural steel truss or cantilever undergoeswhen subjected to load. As a result, the strain set up by stresses inthe one rigid part is not transmitted Wholly to the other rigid partbecause of the deformation or strain, in shear, of the numerous hard orrigid and small crosssec tioned bridging columns [3 and theircross-connections 14. For example, should the rigid part l l in Figs. 1,3, and 4, upon rise in temperature, expand radially outwardly fasterthan does the rigid abrasive annulus H), the hard or rigid parts I3 andit are subjected to vertical shear, as along the vertical plane AA ofFigs. 3 and 4, and they individually deform or bend somewhat, aided bytheir minimum central cross-section, and thus the radial outwardmovement of the expanding rigid part I l is not, or cannot be,completely enforced upon the rigid abrasive part the flexing of thehardened, rigid parts l3 and Id of Figs. 3 and 4 thus permits sufficientrelative movement between the two rigid parts It! and H and protects theconnecting means 12 as a whole against actual cleavage under shear. Theconstruction, moreover, has good strength under the pressures of actualgrinding operations, even if those pressures are directed radially orhave radial components; and, where grinding pressures are exerted indirections parallel to the lengths of the individual columns or posts,as for example when exerted in directions toward the right as viewed inFigs. 1, 3, and 4, the junction-forming means 52, that is, the manyindividual posts or columns, has good compressive strength, the hard orrigid material of each of the many bridging increments taking the loadwithout failing.

The connecting pillars or posts I3 are numerous, as above noted, andpreferably uniformly distributed; for example, there may be severalhundred voids or cells per square inch of cross-sectional area along theline 2-2 of Fig. They may, for example, be arranged in some suitableuniform geometric design, such as a checker-board design, with onepillar or post for each individual square which may be dimensioned tohave, say 14 squares per linear inch; in such case there would be about196 connecting elements 53 per square inch. According to ourinvention'we provide an inexpensive and economical way of achieving aconstruction of the above-described character and to facilitate theprovision of a large number of individually small and substantiallyuniformly distributed individual connecting or bridging parts.Illustratively,

when we employ a curable or settable synthetic resinous cement, such asphenol-aldehyderes inous cement, we use the cement in fluid form ofsuitable viscosity and prefer initially to coat each of the faces,indicated at 0 and l respectively, of the rigid parts l0 and H, with oneor more coats of. the cement, and then we provide a suitable means whichcan at once function as a carrier and distributor of such cement orsubsequent applications of cement for the purpose of building up thenumerous increments of uniformly distributed connectingbridges or partsI3 and i4 and to serve also as a spacing means between the two rigidparts is and H in order thereby to give the parts 13 appropriate lengthin a horizontal direction as viewed in Figs. 1, 3, and 6. Such a means,in the form of Figs. 2, 3, and 4, conveniently comprises strands of anysuitable material, preferably arranged in any suitable way, as byweaving, to provide interstices therebetween and of suitable size. Forexample, the strands may be interwoven to form an open mesh fabric, withthe interstices or apertures substantially square, and in Fig. 2 areindicated several horizontal strands H and several vertical strands V soarranged; thus, the material may be made up to have, for example, 14meshes or squares per linear inch, in which case the material would have196 squares or in- 513, wetting it, or it merges 6 terstices per squareinch of area. The spacep carrier then has the resinous cement applied toits strands, and this may be achieved in any convenient manner.

For example, the open mesh structure may have the liquid form of cementpainted onto it, or it may be clipped in the liquid cement, or thelatter may be sprayed onto the strands, the cement 'if necessary beingpreferably given a viscosity appropriate to the character of thematerial of which the strands are made. For example, if the strands aremade of textile fibers, it is desirable to impregnate them as well ascoat thestrands, and in such case higher fluidity may be more suitablethan would be the case if the strands were of a material that need notbe im-- pregnated or that is impervious. Synthetic as well as naturalorganic fiber may be used, and also glass fiber; solid, and henceimpervious, strands are also usable, and these may be of any convenientor suitable material. Strands or stranded materials, if pervious, may beand preferably are first treated in any suitable way so that they willnot have a wicking or capillary action upon liquids such as water, andthis may be done by impregnating them in any suitable way;illustratively they may be impregnated by suitably thin solutions of thesame cementing material that is to be used in making up the connectingposts or pillars or in preliminarily coating the faces of the rigidparts ill and ll.

The open mesh spacer-carrier structure, coated heavily enough with theliquid or plastic cement which preferably does not fill the intersticesthereinand which, if desired, may be partially or completely maturedthereon, is now laid or spread out against one of the rigid surfaces tobe connected together, for example, against the face ll of the rigidpart H, which, as above noted, is preferably first coated with cement.As it is laid in place, and with the face already coated, the liquid orsemi-liquid cement carried by the strands coalesces with the coating onthe rigid surface or wets the latter if it has not previously beencoated, spreading out materially beyond the dimension of the strandsthemselves, and, should one or more interstices of the spacer-carrierstructure have been filled with liquid cement, its contents are drawn tothe rigid surface and spread out or intermingled with other regions ofcement on the surface.

Then the companion rigid part, such as the member if! with its rigidface i preferably coated, is placed on top of the assemblage of therigid part if and the spacer-carrier, whence cement from the strandsattaches itself to the face with the cement coating previously appliedto the face it, and thus the general configuration of the voids or cellsI5 is brought into being, the strands V H of the 'spacer-carrierpreventing where they cross each other at the .apexes of the squares,such close approximation of the two rigid parts it and I! as wouldobliterate the voids and as would make the cement continuous oruninterrupted by voids throughout its entire extent between the tworigid faces W and il. This action of the crossing portions of thestrands V and H, in lim iting the approach of parts it and ii, isindicated in Figure 3 where the cross-sections of the crossing portionsof the strands are shown more or less of oval shape due to thecompressive forces exerted thereon, necessarily at the apexes,

of the square meshes of the spacer-carrier structure where the thicknessof the latter is other- 7. Wise greatest because of the crossing of thestrands at these apexes; in contrast, the lengths of these strandsintervening the apexes are substantially uncompressed as is indicated bythe circular cross-sections of the strands as pertrayed in Figure 4. Theassemblage is then preferably subjected to some pressure,illustratively, on the order of a few pounds per square inch,insufficient to destroy the cells or voids I5, the application of thepressure being primarily to insure the making of good contact between henow plastic or semi-fluid columns or posts 13 (and where desired, alsothe cross-connectors i4) and the rigid faces iii and i I the actioninsuring enlargement of the areas of contact, accompanied also byelongation in the vertical plane AA of Figs. 3 and 4 ofthe cells l5which are prevented from being filled by cement or from beingobliterated by the air that is trapped in them when the companion rigidpart, such as the abrasive annulus lb, was placed in position in courseof assembly. The moderate pressing together of the assemblage lessensthe horizontal dimension of the cells l5, as viewed in Figs. 3 and e,and the resultant compression of the entrapped air has the effect ofenlarging the vertical dimension thereof, as viewed in Figs. 3 and 4,thus, also, contracting the cement of the columns l3 and parts it andsustaining the still plastic or semi-fluid material thereof againstcollapse, aided by the strands of the spacer-carrier structure whichalso functions to limit the approach between the two rigid parts i Eland l i. It is such actions as these that give the individual columns orsupports 13 and cross-connecting parts is cross-sections generally likethose indicated in Figs. 3 and 4, and they may be aided by the facilitywith which the cement wets the rigid surfaces iii and l i, particularlyif the latter are preliminarily coated with cement.

The cement is now allowed to harden and any suitable treatment,depending upon the character of the cement, is here applicable.Synthetic resin cements are available that cure at ordinary roomtemperature; others are available that require some heat treatment, andin such cases the assemblage subjected to appropriate heat treatment toharden the cement. During the cure or setting, the moderate pressureabove mentioned is maintained, and a simple way of doing that is simplyto put a weight upon the last of the several parts to be assembled. Asthe cement sets, the strands H and V become solidly encased or embeddedtherein and in the final structure they need not take part in actionsthat ensue when the completed rigid grinding structure is subjected toforces like those earlier above described.

Or we may employ cements that undergo shrinkage during cure or utilizethe factor of shrinkage which various usable cements are known to have.In such case we apply the ce ment in liquid form to the open-meshspacercarrier element above described in such manner as to be certainthat the interstices are well filled with the liquid or plastic cement;it may be assembled to the rigid parts ill and H, preferably with thefaces thereof initially coated, all in the illustrative manner abovedescribed, and the assemblage then subjected to some pressure, which mayagain be on the order of several pounds per square inch, in order tobring the two rigid parts toward each other to the desired extent, allas limited by the action of the strands as above described.

Curing or setting may then be proceeded with and as the cement cures orsets it shrinks, shrink ing onto or about the strands V and H, and in sodoing creating the voids or cells 15 by the coaction of the strands Vand H with the shrink-- ing cement; by reference to Fig. 2 it will beseen that the strands V and H extend around individual areas orincrements of the rigid surfaces to be joined together, these areasbeing of square shape in the illustration. As the cement shrinks andundergoes movement as the result of the shrinkage, the strands impedesuch movement while the cement within the areas is unimpeded, and henceit is cement within those areas that partakes of movement outwardly awayfrom the center of each area that forms the voids or cells. In otherwords, those portions of the cement that are in these areas and hencenot impeded from partaking of movement are shrunk or moved into ortoward those portions of the cement that are restricted against movementby the strands V and H.

In Figs. 5, 6, '7, and 8 we have shown another embodiment of certainstructural features of our invention and of our method, and referencemay first be made to Fig. '7 in which a fragment of one of the rigidparts such as the part I l is shown in cross-section; to its face II weapply a layer L of the cement in suitable plastic or semi-liquid formpreferably after havin first applied and set a coating of cement to theface H as is preferably done in carrying out the methods above describedin connection with Figs. 2, 3, and 4. With the part II positioned sothat the face H and hence the layer L are horizontal, we now distribute,in any suitable manner and as nearly uniformly as possible, a suitablenumber of pellets or granules G which are preferably uniformlydimensioned or of substantially the same shape and size, made of amaterial having such physical characteristics that the pellets orgranules employed have preferably little or no resistance to shear. Forexample, the material may be cork or rubber so that the pellets orgranules do not transmit substantial shear stresses; such materials canbe comminuted or broken up in any suitable or known way, and they aresized by screening so as to provide substantial equality of size ordimensions. A wide range of materials is available for making thesepellets. By way of further example, the pellets may comprise vegetablematter in the form of certain seeds. For example, poppy seeds which aregenerally spherical, more or less uniformly sized, and capable of sizeselection by screening; individually they appear to have some rigidity,but structurally they have relatively small resistance to shear; Seeds,if employed, are preferably first thoroughly dried and, according totheir nature, may be impregnated if desired.

The pellets G are spread onto the relatively thick layer L of cementwhich preferably is in a form having appropriate liquidity so that itwill wet the pellets, being thereby drawn toward or onto the pelletsfrom the areas or regions intervening the pellets, thinning itself outthroughout such regions somewhat in the manner indicated in exaggeratedform in Fig. 7. The pellets may be distributed in appropriate spacings,for example, 8 or 10 or so per linear inch or about or so per squareinch. The companion rigid part Ill (see Fig. 8) next has its face Hisupplied with a layer L of the cement, preferably after having appliedand set thereon a thin coating of the cement, and with the layer Lthereof facing downwardly, the rigid part it may now be brought downonto the above-described assemblage of the rigid part i l, its cementlayer L and the pellets G held in and on the cement layer L Convenientlythe layer L is of smaller mass or thickness than the layer L and thoseportions of the pellets G that are exposed upwardly are engaged by thecement of layer L and in effect are embedded therein.

Suitable pressure, on the order of several pounds per square inch, maynow be applied to bring the two rigid parts l0, ll together to thedesired extent, effectively limited by the uniform vertical dimensionsof the pelletsG as viewed in Figs. '7 and 8. Curing or setting may nowbe proceeded with. v

If the cement in layers L and L is applied in insufficient quantity tofill all of the space about the pellets G and inbetween the two rigidparts and Il, voids I are again formed inasmuch as the cement of onelayer can join itself to the cement of the other layer only through themedium of the pellets G, the surfaces of which the cement envelops. Thepellets G, in this mode of carrying on this embodiment of our invention,prevent such a close approach of the two rigid faces 16 and H as wouldpermit the cement of one layer joining with the cement of the otherlayer throughout their entire areas.

On the other hand, we may employ, for the layers L and L of Figs. '7 and8, cements having the shrinkage characteristics above mentioned andapplythem in greater quantity than just described, namely. a quantitysufiicient to fill all of the space between the two rigid faces lll andli as the volume of that space is determined by the action of thepellets G in limiting the approach of the two rigid faces H3 and Htoward each other. When cure or setting proceeds, the cement shrinks andagainthose portions that are unimpeded shrink or move to those portions,namely the portions of the cement, about the 5 functions as abovedescribed. It is economical? to manufacture from the viewpoints of bothstructural elements and procedural steps employed. The multitude ofrelatively small cross-v sectional areas of junction between the tworigid parts are easily and withfacility achieved, par-- ticularly whenthere is employed the unitary stranded spacer-carrier structure likethat of Figs. 2, 3, and 4, the strands of which, accord sembled of themultitudinously distributed increments of cement, 'care being taken thattheamount of cement in fluid form be appropriately proportioned, as willnow be clear, to the sizes pellets G that are restricted or held frommigration by the pellets themselves.

In either case the structure, when cure or setting is completed, appearsin general as isshown in Figs. 5 and 6 wherein the individual pillars orcolumns are indicated by the reference character I3 each column havingwithin it and encompassing a pellet G which is solidly encased andembedded in the cement. The columns or supports it will be seen to beindividual or uniformly distributed; they are rigid and strong, and. intheir action absence of resiliency therein is not detrimental. formlysized pellets, they are of substantially uniform effective crossse'ctionso that each does the same amount of work as any other. Furthermore, dueto such actions as those above described, the pellets are effective togive the joining posts or columns 13 cross-sectional areas as viewed inFig. 6 which are progressively increasing in both directions away from acentral Vertical'plane indicated at AA in Fig. 6; they are thusoutwardly divergent in cross-section, and each part presents tothe facesof the rigid parts I!) and I! greater areas for strong bonding or'adhesion than is its minimum cross-sectional area. In that manner alsothe entire areas of the adjacent faces NB and H of the rigid parts maybe utilized for achieving maximum area of junction of the securing meansiii to the adjacent faces. H

" Elhe'resultant structure of either Fig. 2 or Fig.

By using substantially uniof strands and the sizes of the meshes orinterstices in the carrier struc ure.

four inches, a suitable and illustrative spacercarrier to employ ismosquito netting of about 16 mesh.v The thickness of the strands, thema-" terial thereof, and the size of the interstices of thespacer-carrier may bewidely varied accordof the pellets may be widelyvaried according to circumstances, as will now alsobeunderstood It willalso be understood that thoughthe rigid abrasive part I0 is abovedescribed as vitrifiedbonded, our invention is not limitedtovitrifiedbonded abrasive structures, but' 'that the rigid abrasivestructure may embody any other suit able or known bonding medium or bondstructure; also the description of the rigid'part I as: of metal is notto be interpreted as a limitation,- since that part may be of any othersuitable ma terial, for example, powdered aluminum bonded by resin or aresinoid. In any such cases', 'where forces or stresses of the kindearlier above 'me'ntioned are brought into play, due principally 'todifferences in thermal coefficients of expansion," or to centrifugalaction," their detrimental effects may be reliably overcome according toour-in vention. 3 5

Because of the unique actions of the individ-E ual increments ofbridging connectionfprovided by parts like the parts l3 and M when sub--jected to shear, we areenabled, if desired, to carry out our inventionin a manner to give theserigid bridging increments agreater range 0?action. Thiswe may do by using a cement in terial that requiresapplication of heat to'cu're and harden it so that the heat treatmentasifi an oven, of the assembly raises the temperature of the rigid partsI!) and l I to expand them to the different extents according to theirrespective temperature coeffi-cients of expansionklri such case, if themember H of Fig. 1 is the one that has the higher temperaturecoefficient, thj bridging increments is or 13 and the like are} set andhardened to rigid condition to secure the two rigid parts Ill and IItogether in their differentially expanded condition. Upon coolingoff,the twoparts contractto respectively diff ferent dimensionscorresponding to normal -or room temperature, and the many bridging orsecuring increments are thereby "strained to-put the rigid abrasive partH! in compression,- the forces of compression acting radially inwardlyin-a direction to tend to reduce the radii of-the part lllglthecompanion rigid part I i would-Basa 'r'es'ult; be in tension. When theresultantfg-rind- For small-diamx-t: etered grinding wheels, on theorder of three or ing" wheel is then put into use, it rises intemperature, due to the heat generated under the abrading action of therigid abrasive part H, and the latter expands, as does also the rigidpart H, as temperature equilibrium throughout the entire structure isreached, and hence the initial strain to which the securing columns orposts are subjected becom'es" relieved, in whole or inpart, so that theoperation of the grinding wheel can continue with shear stresses, due todifferent temperature coefficients of the parts it and I I. in whole orin part'eliminated from the connecting columns or increments. The lattercan thus better cope with the stresses otherwise imposed by the rotationof the grinding wheel and its grinding operation."

. A preferred manner in carrying out this aspect of our invention is toutilize a cementing material that cures at a temperature above roomtemperature but substantially at or below the intended operatingtemperature of the abrasive structure; for the latter, the upper limitis usually around 100 0., the boiling point of water, which isfrequently employed as a coolant in grinding operations. We prefer toemploy a cement that cures at a temperature intermediate ofthe operatingtemperature of the grinding wheel and room temperature, those being theupper and lower temperature extremes to-which the abrasive structure issubjected in ordinary use. preferred and illustrative curing.temperature is in the neighborhood of 65 C. and various syn thetic resincements curable at this temperature as well as cements curable withinthe preferred range above mentioned are available.

With a cement that hardens or matures at this intermediate temperature,the connecting posts or columns It or iii become set when the two rigidparts, whatever their differences in thermal coefilcients, aredimensionally less changed relation to each other than if thetemperature of maturing or curing were outside of the normal or ordinaryrange of change of temperature of the ultimate abrasive structure; upon.cooling down to room temperature, comparatively small relativedimensional change of the rigid parts l and H takes place, subjectingthe connecting posts or columns to a correspondingly small strain orbending in one direction. At around room temperature, therefore, theconnecting posts are normally under some strain, a strain which becomesless and less as the grind ing structure warms up when it is put intooperation. When the abrasive structure-reaches the temperature at whichthe material of the connecting columns was matured, for example, atemperature of 65 0., the columns are free from strain caused bydifierentials in. thermal coefiicients, and as the. temperature of theabrasive structure continues to rise to, for eX- ample, 100 0., tooperating temperature, the columns are strained in opposite directionsbut to a far lesser extent than would be the case if the entire rise intemperature had beenedective to cause strain in the same direction. As aresult it is possible to cut the range of change of strain in theconnecting columns down to about 50%.

As earlier above noted, however, so-called air drying cements, namely,compositions that cure at ordinary room temperature, may be employed incarrying out ourinvention.

{The junction I2 ofFig. 1, being made up of a large number of columns orposts-isee Figs. 3, 4, new ha a le ser capacity; -.seadu ve f.

heat from the abrasive part It to the rigid sup porting or backing partH than it would have if its resinous composition were solid throughoutthe entire junction; the cross-sectional area' of the junction (seeFigs. 2 and 5) is materially less than its cross-section would be wereit to be solid throughout, and hence conduction of heat does not soreadily take place. This lower capacity for heat transmission'isenhanced also by the voids or hollow spaces 1 5 in Fig. 2 and by theconnected spaces I5 of Fig. 5, and may also be aided by the material ofwhich the parts H and V of Fig. 2 or the parts G of Figs. 5 and 6 aremade, if such material is selected to have a heat conductivity less thanthat of the cement composition employed. Hence a substantial temperaturedifierential is maintainable between the part 19 and the part i i, sothat the part H, if it is the part of higher. thermal coeflicient ofexpansion, partakes of diminished increase in its dimensions, and theconnecting posts or columns of the junction l2 are subjected to acorrespondingly less strain or deflection. Where the junction. i2 is ofthe kind described in connection with Figs. 5 and 6, the spaces betweenthe connecting columns 13 are all connected and open to the atmosphere,bothat the inner and at the outer circumferences of the junction l2 (seeFig. 1), and thus heat-withdrawing movement or circulation of air fromthe atmosphere can take place therethrough, and, when embodied in agrinding wheel form as shown in Fig. I centrifugal forces aid indischarging such heat-withdrawing air from the outer periphery of thejunction 12, fresh air as a result being drawn radially inwardly of thejunction l2 at its inner circumference. Such air cooling throughout thejunction further lowers the rate of possible heat transmission from theabrasive part i 9 to the companion part II, thus enhancing theabove-described advantageous result. If a liquid coolant is employedduring the grinding operation, an analogous action takes place inforcing the liquid coolant centrifugally through the connected spaces inthe junction, often-times materially aided by the above-describedmovement of air therethrough where the liquid coolant is concentratedprincipally at the point or line of grinding contact of the abrasivepart with the Work-piece being ground. Strain of the junction,' due tothermally responsive dimensional changes in the joined-together parts,can thus be greatly reduced. Generally similar coactions and advantagesare achievable where the junction [2 is of the kind described inconnection with Fig. 3 the spaces or cells I5 being interconnected andopen to the atmosphere, both at the inner and outer circumference of thejunction l2 (see Fig. l), the interconnection of the spaces 15 beingeffected, as above described, by the gaps (see Fig. 3 between thecross-connecting webs M and the respective faces of the two rigid partsI!) and II.

By providing a series of successive heat-barrier junctions in the pathof flow of heat from the abrasive surface to the part II, We are enabledto provide an abrasive structure of improved action and of certaindesirable unique coactions amongst its several parts, as isillustratively shown in Fig. 9, in which the abrasive part 1 0 maycomprise a structure having a vitrifled-bonded diamond abrasive layer Wand a vitrified-bonded body portion "l such as de scribed above inconnection with Fig. 1, and a rigid part II, such as that abovedescribed; in-

terposed between the two parts l and H of Fig. 9, however, are severalheat-barrier junctions l2, illustratively three in number, alternatedwith one or more, illustratively two, rigid parts P and P preferablyconstructed and composed in the same manner as the part It", and hencebeing also vitrified-bonded, conveniently and illustratively comprisingsuitable granular body material such as fused alumina, vitreous silica,feldspar, clay, or the like, a suitable bond of a Suitable glass, theparts l0 and P and P being preferably of similar composition and havingthe same thermal coefficient of expansion. The succession of parts, asindicated in Fig. 12, are socured together by junctions l2 constructedpreferably in the manner and with structural features illustrativelyabove described, and the intermediate parts such as parts P and P may beemployed in any number and in any desired axial dimension or thickness.For cup wheels of substantial or large depth or axial dimension, theinterposed parts may be relatively thick axially and may be made up ofuniform dimensions to thus lend themselves to facilitate of building upa cup Wheel of any desired axial depth. Where the cup wheel isrelatively shallow as in Fig. l, the part I!) may be made up in smalleraxial thickness and likewise the interposed part or parts such as partsP and P in order, within the shallow cup depth, to get the desirednumber of heat'barrier junctions l2.

Each of the succession of junctions l2, functioning thermally as abovedescribed, can thus be effective to maintain a substantial tempera t redifferential between the parts which it secures together, so that theusually substantial rise in temperature of the abrasive part Hi, fromroom temperature to operating or grinding tem perature, is step by stepprecluded from being communicated to the mounting or supporting part itwhich, if made of metal or other mate rial having a markedly differentthermal coefficient of expansion, is thus precluded'from partaking ofsubstantial dimensional changes and hence from subjecting its immediatejunction !2 to substantial strain. Though the overall temperaturedifferential, that is, between the part It] and the part H of Fig. 9,may thus be substan tial, the succession of interposed heat-barrierjunctions has the effect of subdividing that overall temperaturedifferential into a succession of fractional temperature differentialsbetween the successive rigid parts, so that their respective junctionsare subjected to but fractional strains due to their relativedimensional changes. These actions, moreover, are of amplifying ormultiplying effect in the direction from the part of high esttemperature to the part of lowest temperature, since the rate of heatflow through any one junction is a function of the difference betweenthe absolute temperatures of the two parts joined together, and in eachcase that difference is but a fraction of the difference in temperaturebetween the parts it and l I. By such cumulative coaction of parts suchas those just described, we are enabled with safety and efficiency "andeconomy to cope with large temperature dife 'ferentials between theparts it and H of substantially different thermal coefficients ofexpansion, illustratively with the part H having the higher coefficientof the two.

Though in the illustrative embodiments above described we haveillustrated our invention with lrlc'spectto a grinding wheel,..theinvention .is to be interpretedas embodying, or as applicable to,

any other abrasive articles, such as an abrasive stick, wheel segment,or the like, for which it is desired to achieve the many advantages ofthe invention, and in the claims the term grinding wheel, unlessotherwise qualified, is therefore to be interpreted to include any suchabrasive article.

It will thus be seen that there has been provided in this invention aconstruction and method of achieving the same in which the variousobjects hereinbefore noted, together with many thoroughly practicaladvantages, are successfully achieved. The junction or joining meanseffected according to our invention, though comprising individualresinous cement parts, can be made to have advantageously a low modulusof elasticity, being as a joint less rigid than the rigid abrasivemember It that is oined to another rigid part;

havinga low modulus of elasticity, it can deflect under stress, yet theiniividual hard and relatively rigid connecting columns undercompression do not permit of relative out-of-truth shift of one of theparts relative to the other as has been known to happen, under somegrinding conditions, where the two parts are secured together 'byresilient cement as has heretofore been used in the endeavor to overcomethe difijcu ties posed by the different thermal coefiicients ofexpansion.

With our invention we are enabled to employ cements which mature to ahard and relatively rigid condition and to cause them to function, underthe peculiarly difficult and changing conditions wrought by thesubstantial and otherwise uncontrollable stresses and strains broughtinto being by centrifugal forces and by thermal changes, not onlydependably to secure the two rigid parts together but also to lessen, oravoid, risk of failure, as by rupture in shear as could happen accordingto prior attempts to utilize such cements.

It will thus be seen that there has been provided by this invention anarticle and a method in which the various objects hereinabove set forthtogether with many thoroughly practical advantages are successfullyachieved. As many possible embodiments may be made of the mechanicalfeatures of the above invention and as the art herein described might bevaried in various parts, all without departing from the scope oftheinvention, it is to be understood that all matter hereinabove setforth or shown in the accompanying drawings is to be interpreted asillustrative and not in a limiting sense.

We claim:

1. A grinding Wheel comprising a rigid abrasive part and a rigidsupporting part adapted to be rotated, said two'parts having differentthermal coefficients of expansion and therefore responding withdifferent dimensional changes. to changes in temperature throughout therange from normal or room temperature to grinding wheel operatingtemperature, said two rigid parts having adjacent spaced surfacesthroughout which they are secured together, and means securing said tworigid parts together and permitting relative dimensional changes to takeplace therebetween in response to thermal changes and to centrifugalforces, said means comprising an initially substantially plasticcementitio s material maturable at a temperature intermediate of theaforesaid iimiting temperatures of said temperature range, saidcementitious material being matured at said intermediate temperature,and with both of said rigid parts raised to said intermediatetemperature, to a sub stantialiy rigid condition in the form of a D 1-rality of distributed and spaced compression-resistant masses of saidmaterial matured to said rigid condition and bridged between and joinedat their respective ends to said spaced adjacent surfaces of said twoparts whereby said rigid masses, upon the latter and saidjoined-together two parts reaching normal or room temperature, areindividually strained in shear in one direction and, upon subsequentrise in temperature to grinding wheel operating temperature, areindividually strained in shear in opposite direction.

2. An abrasive article comprising a rigid abrasive part and a rigidsupporting part, said two parts having different thermal coemcients ofexpansion and therefore responding with different dimensional changes tochanges in temperature throughout the range from normal or roomtemperature to operating temperature, said two rigid parts having spacedfaces throughout which they are secured together, and means securingsaid two rigid parts together comprising at least one interposed rigidpart to provide a pluralit of pairs of adjacent surfaces throughoutwhich the k parts are to be secured together and a securing meansbetween and joining together each pair of adjacent surfaces of saidplurality of parts, the securing means being made of a maturedcementitious material and having relatively low heat conductivity andthereby interposing a plu-, rality of barriers between said rigidabrasive part and said rigid companion part and each resistive of thetransfer of heat therethrough and thereby oppose lessening of thetemperature differential between said last two mentioned parts.

3. A cup type of grinding wheel comprising a plurality of bonded annuliadapted to be superimposed in a series one upon another in axialdirection, the bonded annulus at one end of the series comprisingabrasive grains and presenting an abrasive face for grinding and a rigidsupporting part adjacent the annulus at the other end of the series,said supporting part and said end abrasive annulus having difierentthermal coefficients of expansion, and means forming junctions betweenthe adjacent faces of said annull and between the adjacent faces of saidsupporting part and of the bonded annulus at the other end of saidseries, said junction-forming means comprising matured cementitiousmaterial, and means giving the junction-forming means a lesser heatconductivity than the heat conductivity of the matured cementitiousmaterial per se, thereby to interpose between the abrasive annulus andthe supporting part a plurality of serially related barriers resistantto the flow of heat.

4. A cup type of grinding wheel comprising a plurality of bonded annuliadapted to be superimposed in a series one upon another in axialdirection, the bonded annulus at one end of the series comprisingabrasive grains and presenting an abrasive face for grind ng and a rigidsupporting part adjacent the annulus at the other end of the series,said supporting part and said end abrasive annulus having differentthermal coefiicients of expansion, and means forming junctions betweenthe adjacent faces of said annull and between the adjacent faces of saidsupporting part and of the bonded annulus at the other end of saidseries, said junction-forming means comprising an initiallysubstantially plastic cementitious material maturable ata temperatureintermediate in the range from normal or room temperature togrindingwheel operating temperature, said cementitious material beingmatured at said intermediate temperature and with all of said annuli andsaid supporting part raised to said intermediate temperature to asubstantially rigid condition in the form of a plurality of distributedand spaced relatively rigid securing elements of said material maturedto said substantially rigid condition and cementitiously joined at theirrespective ends to the respective adjacent surfaces whereby saidsecuring elements, upon the latter and said joined-together annuli andsupporting part reaching normal or room temperature, are individuallystrained in shear in one direction.

5. The steps in a method of making a grinding wheel that comprises arigid abrasive part and a rigid companion part that has a differentthermal coefficient of expansion than said rigid abrasive part with atleast one rigid part interposed therebetween, said steps comprisingarranging said parts serially and interposing between adjacent surfacesof successive parts a combined carrier and spacer means comprising anopen-work fabric of which the strands carry cementitious material ininsufiicient quantity to completely fill, upon setting, the intersticesbetween said strands, and treating the assemblage to set thecementitious material and thereby join successive parts together,whereby the said cementitious material has distributed substantiallyuniformly therethrough a plurality of hollow spaces to lessen theeffective heat conductivity of the resultant junction below that whichit would have were it of solid cementitious material, thereby tointerpose a series of barriers resistive to flow of heat between theendmost members of said serially-arranged parts.

6. The steps in a method of making a grinding wheel that comprises arigid abrasive part and a rigid companion part that has a differentthermal coefficient of expansion than said rigid abrasive part, saidsteps comprising placing between and in contact with the adjacent spacedsurfaces of the two parts a plurality of substantially uniformlydistributed relatively small masses of an unmatured cementitiousmaterial that is maturable at a temperature intermediate ofroomtemperature and grinding wheel operating temperature, holding thetwo parts in spaced relation, maturing the cementitious material of theplurality of masses by heat-treating the assemblage at said intermediatetemperature to thereby dimensionally change said rigid parts torespective values corresponding to temperature increase thereof to saidintermediate temperature and to mature said masses in the form of aplurality of distributed and spaced securing elements bridged betweenand joined at their respective ends to the adjacent surfaces of saidrigid parts, and then cooling the assemblage to room temperature wherebysaid securing ele ments are individually strained in shear in onedirection by the resultant relative dimensional changes in said tworigid parts.

7. The steps in a method of making a grind: ing wheel. that comprises arigid abrasive'part and a rigid companion part that has a differentthermal coeflicient of expansion than said rigid abrasive part, saidsteps comprising placing between adjacent surfaces of said parts anunmatured cementitious material maturable to role-'- tivelyrigidcondition at a temperature inter,- mediate of room temperature andgrinding whee] operating temperature, heating the resultant as semblageto said intermediate temperature to thereby effect correspondingrelative dimensional change between said two rigid parts and to maturesaid cementitious material at said intermediate temperature and rigidlyjoin together said two parts of the grinding wheel while dimensionallychanged due to temperature increase to said intermediate temperature,and cooling the resultant assemblage to room temperature whereby thejunction formed by the matured cementitious material is strained inshear in one direction and upon subsequent rise in temperature,

to grinding wheel operating temperature is strained in shear in oppositedirection.

8. A grinding wheel comprising a rigid abrasive part and a rigidcompanion part adapted to be rotated, said two parts having differentthermal coeificients of expansion and having adjacent spaced surfacesthroughout which they are to be secured together, and means securingsaid two rigid parts together and permitting relative dimensionalchanges to take place therebetween, said means comprising an initiallysubstantially plastic cementitious material matured to substantiallyrigid condition in the form of a multiplicity of diminutive individuallysmall-crosssectioned and substantially uniformly distributed hardenedand rigid compression resistant elements bridged between said space-dadjacent surfaces of said two rigid parts and with their axessubstantially at right angles to said adjacent surfaces, each elementbeing bonded at its respective ends to said two surfaces, saidcementitious material having embodied therein smalldimensioned spacerelements comprising a pluthat take place between said two rigid parts inthe general directions of their adjacent surfaces into a multiplicity ofstrain effects respectively at said small-cross-sections thereof of amagnitude insufficient to cause rupture'in shear.

9. A grinding wheel comprising a rigid abrasive part and a rigidcompanion part adapted to be rotated, said two parts having differentthermal coefficients of expansion and having adtributed hardened andrigid compression resistant elements bridged between said spacedadjacent surfaces of said two rigid parts and with their axessubstantially at right angles to said adjacent surfaces, each elementbeing bonded at itsrespective ends to said two surfaces, saidcementitious material having embodied therein small-dimensioned spacerelements comprising a plurality of individual pellet-like memberssubstantially uniformly dimensioned to effect substantially uniformspacing between said two spaced surfaces of said two rigid parts andsubstantially uniformly distributed between the lat ter, saidpellet-like elements being individually enveloped by and encased withinthe matured cementitious material, said small-dimensioned spacerelements serving, while the cementitious material is in initial plasticcondition, to space said two rigid parts from one another andsubstantially to determine the axial length of said compressionresistant elements in the direction from one of said spaced surfaces tothe other, said multiplicity of small-cross-sectioned hard and rigidelements converting stresses caused by relative dimensional changes thattake place between said two rigid parts in the general directions oftheir adjacent surfaces into a multiplicity of strain effectsrespectively at smallcross-sections thereof of a magnitude insufficientto cause rupture in shear.

LOWELL H. MILLIGAN,

\ ROBERT H. LOMBARD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,767,821 Thompson June 24, 19301,970,835 Benner Aug. 21, 1934 2,048,905 Webster July 28, 1936 2,065,941Lane Dec. 29, 1936 2,065,942 Lane Dec. 29, 1936 2,070,764 Webster Feb.16, 1937 2,353,864 Wooddell July 18, 1944 2,379,544 Scutt July 3, 19452,479,078 Milligan et a1. Aug. 16, 1949

